Sending Letters by Airmail from America

I had studied in New York to learn English for three months.
While I was there, I sent many letters by airmail (There wasn't e-mail and the internet! It took four or five days to send a letter from America to Japan. It is a story from the Stone Age) to my wife (who wasn't my "wife" at that time).
At first I wrote letters in Japanese. After I began getting used to writing things in English, my letters became a mixture of English and Japanese. The proportion of English was increasing, and by the end I wrote letters only in English.
When I think something in English, something written in English fits my feeling more than in Japanese.
To write natural sounding English, it might be better to think and write in English than to think and write in Japanese and translate into English.
Anyway after I wrote a journal on my weblog in English, I bother to translate it into Japanese. But Japanese readers of my weblog (who are almost all of readers) will go away, if I write a journal only in English. I am disturbed about this problem.